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PALEOMAGNETISM OF EARLY ROCKS OF THE DE LONG ARCHIPELAGO AND TECTONICS OF THE TERRANE Metelkin D.V., Chernova A.I, Trofimuk Institute of Petroleum Geology and Geophysics SB RAS Matushkin N.Yu., Vernikovsky V.A. [email protected] Novosibirsk State University

Novosibirsk, Paleotectonic reconstructions for 520-440 Ma Abstract 520 Ma Jeannette Island North NSI The De Long archipelago is located to the north of the Anjou archipelago as a part of a Paleoasian30 O hemisphere hemisphere 30 O large group between the Laptev and , the New Siberian OM Paleoasian ocean . Islands and consists of Jeannette Island– and the tTwhose tectonic history was independent of other, hese islands have been shown CH CH Siberia o be part of a single continental terrane Paleomagnetic and precise geological data for the De Long equator De Long archipelago were. continental masses at least since the special inter Archipelago nnational field trips to the could be organized and geological???? Only i NSI OM Laurentia . absent until recently, geochronological and paleomagnetic studies were carried out-isot Kara Laurentia Kara .ope Baltica 30 30 O O Iapetus ocean Baltica aOThe age of these dikes is more. sedimentary sequence intruded by mafic dikes w Svalbard New Siberian Islands Svalbard s described-n Jeannette Island a volcanic Ar and paleomagnetic investigations of the/ a Iapetus ocean s evidenced by the results of our Ar, Ma48? close to , likely Early Ordovician there are wid 60 O 60 eespread, On Bennett Island. dolerites as well as the result from detrital zircons in th Bennett Island O Gondwana host rocks published before Paleomagnetic results from these rocks characterize the pale Gondwana ogeographic. Ordovician mainly terrigenous rocks- although there is no evi ndence for the primary origin of, Ma5?? Ma and perhaps at 465 position of the De Lo g archipelago at A. sedimentary section was investigated-On Henrietta Island the Early 480 Ma Cambrian volcanic. magnetization for the latter Adding to our previous paleomagnet ic. Ar results/ Ma was obtained and confirmed by new Ar5?? paleomagnetic pole for data NSI

for the Anjou archipelago the extended variant of the apparent polar wander path for the OM 30 30 O New Siberian Island terrane was degrees4? The established paleolatitudes define its O Paleoasian ocean Paleoasian ocean location in the equatorial and subtropical zone no higher than . created Because there are CH u no good confirmations for true polarity and related geographic hemisphere we. d Henrietta Island CH ring the Early Paleozoic But both these solutions demonstrate a very close paleogeographi equator Siberia Siberia c position. present two possibilities for tectonic reconstruction between the New Siberian Laurentia equator Laurentia .Island and the Siberian

The study was supported by Ministry of Education and Science of the Russian Federation Iapetus ocean OM Kara Kara (5????4????7grant No ), RSF (grant ?4-?7-?????No ), RFBR (?5-?5-??4?8grant No ). Iapetus ocean NSI

30 O Svalbard Svalbard 30 O Rheic ocean Rheic ocean Geological maps of Bennett, Henrietta and Jeannette158 IslandsO00’ E Baltica O O O Table. Mean paleomagnetic directions, paleomagnetic poles coordinates and paleolatitudes based on 149 00' E 149 20’ 156O26’ E 156 39’ E. Baltica 60 O QIV 2 km paleomagnetic study of Early Paleozoic archipelagos Anjou and De Long, which used for the NSI 60 ˆ 1 Jeannette Is. O Polar st. Dyunbar cape N Porphyric diorite and QIV Henrietta Is. APWP Bennett Is. K1 Pz tg subvolcanic O 1 km 2-3 45 1-2 2 O Pavel Keppen Objects, Geographic coordinates Stratigraphic coordinates Paleomagnetic poles Gondwana Gondwana 75 43' K1 Unexplored area Plat K Basalts ? n/N N 1 bay Bennetta cape age O O D I k a95 D I k a95 PLat PLong A95 2 2 3 O 65 1-2 Tuffaceous gravelites, Q 60 Koteny Is., 43/45 440 Ma O IV K 1 208.3 81.5 87.0 9.9 272.0 53.9 558.5 3.9 33.7 55.7 5.1 34.4 60 1 4 50 13NS01 36 (4) 11NS10 76O47’ N 440 Ma 13NS02 34 11NS11 70 K1 25 Tuffaceous siltstones Paleopacific 41 Bennett Is., sandstones 25/33 K Pz2-3bz 72 Paleopacific 11NS12 1 5 13NS03 2 298.5 54.1 109.3 11.9 307.7 57.4 178.4 9.3 45.5 31.9 11.0 38.0 Zeeberg Glacier 5 45 465 Ma (3) and polymictic 30 35 40 NSI O K Pz2-3tg 31 1 Q 42 30 O 30 IV 6 sandstones, shales 1 km Kotelny Is., dolomites 23/25 17 3 278.3 77.5 25.7 51.4 315.6 59.1 414.0 12.3 48.9 13.8 18.1 39.9 (2) O 13NS12 18 475 Ma 75 40' O 13NS04 dolerite dykes OM 13NS10 1-2 Pz kp unit 1, volcanogenic-clastic turbidites, Chernyshev 7 1 13NS05 dolerite dikes 13NS11 sandstones, gravelstones, tuffs; Jeannette Is., dolerites, 39/45 36.5 CH pen. Pz bz Pz1ta 4 308.7 44.8 55.5 16.7 344.4 56.0 468.7 5.7 49.2 357.4 5.9 CH 1 13NS07 480 Ma (3) Siberia 8 13NS08 thrusts faults: Siberia O2 ˆ QIV 13NS06 unit 2, mainly breccias; Pz ta N of uncertain kinematics (a), Henrietta Is., sandstones, ˆ 18 2-3 b O2 K Pz2-3tg 56/65 1 a c upthrow-thrust kinematics (b) 5 tuffs, basalts 294.5 25.4 19.0 14.2 295.5 34.0 282.0 3.6 23.7 45.7 3.2 18.6 Sophia cape 10 paleomagnetic unit 3, volcanogenicclastic (6) Paleoasian ocean inferred faults (c); 520 Ma PaleoasianKazakhstan ocean Kazakhstan 6 8 sample sites turbidites and tuff breccias; Kara equator 1 – Cambrian deposits; 2–3 – Ordovician deposits; 4 – 11 3 Kara equator 70 50 Pz kp 12 Bennett Is., sandstones 18/22 deposits; 5 – Cretaceous basaltic covers; 6 – Paleogene- 1 13NS09 unit 4, coarse-grained volcanogenic paleomagnetic 6 (2) 247.8 46.5 184.3 18.5 249.2 37.0 265.1 15.4 15.5 83.6 18.0 20.6 O 530 Ma deposits; 7 – fauna findings; 8 – paleomagnetic 156 39’ E -clastic turbidites; sample sites Svalbard sampling sites. Svalbard Laurentia OM Paleomagnetic study results Laurentia Uralic ocean NSI Uralic ocean Site 13NS07 APWP for NSI terrane Baltica Site 13NS04 Site 13NS01 Baltica O Site 11NS11 N,UP N UP N UP N N,N 30 O 30 N Upper N Upper Upper N Upper Lower Lower Iapetus ocean Lower Lower 630 °C 120 mT Mean paleomagnetic directions NRM ChRM 1213 600°C New Siberian Islands (NSI) Rheic ocean N Rheic ocean NRM NRM Upper NRM ChRM Lower 400 °Ñ ChRM 60 O [Vernikovsky et al., 2013, Middle Lower-Middle 60 Lower NRM Metelkin et al., 2016] Laurentia Cambrian O Ordovician Upper [Cocks, Torsvik, 2011] 250 Gondwana Gondwana Sample 11NS141 E,E Sample 13NS054 E 250 630 °C 360°Ñ 475 270 Upper Ordovician- Bazalt E 400 °Ñ 480 270 Lower Silurian 465 290 Mmax= 55.6 mA/m Sample 13NS085b Mmax=0.24 ìA/ì 460 °C E Mmax= 266 mA/m Mmax=0.69 ìA/ì Paleotectonic reconstruction in which two possible scenarios of NSI terrane position in the Early Paleozoic are presented: on top - N-scenario 1 1 1 1 Lower Cambrian Tuff E Sample 13NS011 440 310 120 mT E,UP for nothern hemisphere, on bottom - S-scenario for southern hemisphere. NSI - New Siberian Islands terrane, OM- Omulevka terrane, CH - 600°C Tilt Dolerite 320 440 corrected 9 mT 370 Chukchi- terrane. 180 °C [Zhdanova et al., 2016] 470 460 350 N-scenario supposes the normal polarity of geomagnetic field while rocks forming and placing the NSI terrane in the northen hemisphere. Such

M/Mmax NSI 520 M/Mmax M/Mmax NRM M/Mmax 490 ChRM 405 Sample 13NS085b 530 400 an option is advantageous because of the minimum horizontal displacements of the terrane resulting from the analysis of the entire set of NRM 515 Equator NRM 430 400 °Ñ 0 0 paleomagnetic data. At the other hand, in this case in the Early Cambrian it should be over a significant distance from Verkhoyansk margin of 0 60 120 mT 0 200 0 315 630 °C 0 300 600 °C [Chernova et al., 2017] 440 530 Baltica [Torsvik et al., 2012] Siberia with which there was a obvious biogeographic link at that time. We assume that this space could be occupied by Omulevka and probably Upper Site 13NS11 W,UP Upper N N UP Upper Site 13NS09 N UP N Site 13NS02 Upper N Preliminary, not published results 450 Lower Site 13NS05 Lower Lower N,N Lower Chukchi-Alaska continental terranes which enabled the fauna to migrate along the shelf. In the Ordovician it is supposed the disintegration this (Bennett Islands Cambrian sandstones) 460 NRM 470 system and further convergence with the Siberia. The downside of this model is that such NSI position is to far from Baltic which is supposed as NRM 540 500 NRM 500 a main provenance area of detrital zircons (Ershova et al., 2016) and this fact should be sought for another explanation. ChRM 600°C Siberia 1 Poles for De Long Islands [Cocks,Torsvik, 2007] 520 The second variant (S-scenario) assumes a more typical for the early Paleozoic reverse polarity of the geomagnetic field and the southern NRM NRM Poles for Anjou Islands 520 80 mT position of the NSI terrane. In accordance with the paleomagnetic data, together with the Omulevka terrane, it could be located near its current 440 °Ñ Sample 13NS64 E 620 °Ñ position, but under another orientation relative to Siberia that gives the explanation of the fauna similarity of the Verkhoyansk and NSI Bazalt E 655 °C ChRM NRM APWP for the NSI in comparison with APWPs of Siberia, Laurentia and Baltica. 600 °C sedimentary basins. In this configuration, the NSI terrane could also be in a close proximity to western , which could be the 620 °Ñ The Ordovician-Silurian poles were discussed in [Metelkin et al., 2016] and they suggest the idea Sample 11NS125 Mmax=0.50 ìA/ì Mmax= 2.36 mA/m ChRM Sample 13NS100 Mmax= 57.7 mA/m Mmax=0.72 ìA/ì provenance area for detrital zircons that are demolished probably from the territory of the Baltic (Ershova et al., 2016). However, global 1 1 about terrane history of NSI block. Here also we can see that pole for Jeannetta Islands dolerites is 1 Sandstone 1 paleogeographic constructions impose certain limitations on this model. At the beginning of the Ordovician, as a result of the Iapetus opening, Sandstone N,N close to Early Ordovician pole for Kotelny Islands deposits but which exactly age reflect the position 480 °C E 480°C of the pole is still debated. We assumed according to our geochronology and paleomagnetic data that the "separation" of the NSI-Omulevka terrane group is reconstructed, which is recorded by a sharp change in the direction of the apparent drift 80 mT E 600°C of the paleomagnetic poles, and then a coordinated movement is expected near the Scandinavian margin of the Baltic. The main problem of this Sample 13NS026 E,UP the these dikes were formed in the Early Ordovician (Zhdanova et al., 2016). The 520 Ma is the rough M/Mmax M/Mmax ChRM M/Mmax M/Mmax 12 mT Dolerite age of sedimentary and magmatic rocks of Henrietta Is. from which the paleomagnetic pole was option is the "too" southern paleomagnetic position of the NSI terrane recorded by paleomagnetic data while Iapetus closing. Already 440 180 °C calculated (Chernova et al., 2017). And also we present the preliminary result on Early-Middle million years ago, when the space of this paleoocean was minimal, the NSI block according to this model should be located inside of this NRM 0 NRM 0 0 310 620 °Ñ 0 655 °C 0 40 80 mT 0 300 600 °C Cambrian sandstones of Bennett Island. So such APWP illustrates the smoth movement of NSI convergent system and its further movement to the current position in the global kinematic picture is difficult. The velocities of the Late terrane in subequatorial and up to Early Ordovician the NSI migrated away from the equator Typical results of stepwise AF (alterating field) and T (thermal) demagnetizations for different kinds of rocks on the De Long archipelago. The site numbers are on the geological maps. Paleozoic drift (~ 20 cm / year) are also very significant. To occupy its current position, the NSI block must "catch up" with Siberia, which all with counterclockwise direction and from 480 Ma some event changed its trajectory to the opposite. this time moves north with a clockwise rotation. Here are presented: orthogonal vector plots in tilt-corrected coordinates, closed (open) circles represent vector endpoints projected onto the horizontal (vertical) plane; stereoplots illustrating demagnetization The close proximity of the poles of De Long and Anjou Islands confirms our previous conclusion path during experiments in tilt-corrected coordinates, closed (open) symbols are projected onto the lower (upper) hemisphere; magnetic intensity decay curves. concerning the unified nature of the New Siberian Islands terrane and its independent history. Thus, the geological and geophysical facts accumulated to the present time proves the unity of the Anjou and De Long sedimentary basins, the subtropical position of the NSI terrane at the Early Paleozoic and, from our point of view, more reasonably describes its location in the northern